Which phase of clinical trials is conducted after preliminary evidence suggesting efficacy and typically involves 1,000-3,000 patients to gather safety and efficacy information?

• A. Phase 1 Clinical Trial
• B. Phase 3 Clinical Trial
• C. Phase 2 Clinical Trial
• D. Phase 4 Clinical Trial

Answer: (B)

Phase 3 trials come after there’s preliminary evidence of efficacy and are designed to confirm that the treatment works and is safe in a large, diverse group of patients. They typically enroll about 1,000 to 3,000 participants and are usually randomized, controlled, multi-center studies. This setup provides robust data on how well the treatment works in real-world settings and helps identify less common side effects, information that regulators rely on to judge whether the therapy should be approved and what the labeling should say.

In contrast, early-phase work starts with safety and dosing in small numbers (Phase 1), then tests preliminary efficacy and safety in a larger but still limited group (Phase 2). After a therapy is approved and marketed, post-marketing surveillance (Phase 4) monitors long-term safety and effectiveness in the general population.